The perianal complications of Crohn's disease (CD) seen in children and adolescents include skin tags, anal fissures, fistulae, and abscesses. While these lesions are often chronic and variably responsive to medical therapy, only rarely are they severely destructive. In this report, we characterize the frequency, severity, and clinical course of a highly destructive form of perianal disease (HDPD) that we have noted in a number of children and adolescents with Crohn's disease. A database containing records from 350 children with inflammatory bowel disease was reviewed to identify all children with CD treated between 1970 and 1993. For each, the occurrence or absence of significant perianal pathology, including fistula, abscess, and HDPD, was determined. Pertinent clinical details were recorded for all patients. In addition, the clinical characteristics of those children with HDPD were compiled, and the courses of those with HDPD characterized. A search of the database identified 230 children and adolescents with CD followed for a total of 1,518 patient years. Sixty-seven of these patients (29% of the CD population) had significant perianal pathology. This included 6 with HDPD, 8 with complicated fistulae [rectourethroperineal (1), rectovaginal (1), rectolabial (2), and multiple communicating perineal (4)], and 53 with simple perianal fistulae or abscesses. All six with HDPD had deeply destructive perineal ulcerations, marked undermining of the perineal and perirectal tissues, and copious exudate, and often there was a deeply cleaved or fileted perineum on separating the buttocks. Two children with HDPD had fecal incontinence.